Preheat your oven to 375 degrees Fahrenheit and lightly grease a 9×13 inch baking dish.
In a large bowl, season the ground beef with garlic powder, onion powder, salt, and pepper. Mix thoroughly and form into 6 patties.
In a skillet over medium heat, cook the patties until browned on both sides and set aside (they don’t need to be fully cooked at this point).
In the same skillet, whisk together 1 cup of milk with the flour until smooth. Add the remaining milk slowly, stirring continuously until a gravy forms. Season with more salt and pepper if needed.
Arrange half of the sliced potatoes at the bottom of the prepared baking dish and layer half of the sliced onions on top.
Place the browned hamburger patties over the onions, then cover with the remaining potatoes and onions.
Pour the prepared gravy evenly over the entire dish.
Cover with aluminum foil and bake for 1 hour.
After 1 hour, remove the foil, sprinkle the shredded cheddar cheese on top, and bake uncovered for an additional 15 minutes or until the cheese is melted and bubbly.